How to get IEnumerable(Of DataRow) From DataTable query - vb.net

Question

All the examples I have found of complex grouping of DataTable results that use linq query commands look to have no problems getting an IEnumerable(Of DataRow) object as the result.
However I seem to only get a AnonymousType Enumerator return that I cannot cast to DataTable.
I have workarounds, but would prefer to convert the results to a DataTable, as it looks possible and I may be doing something wrong.
It's a simple table with Many ClientID and ClientName columns and other columns with login timestamps.
Dim dtMatrix As DataTable = New DataTable()
... (populate DataTable)
Dim qClients = From row In dtMatrix
Group row By client = New With {Key .ClientID = row("ClientID"), Key .ClientName = row("ClientName")} Into Group
Select New With {Key .ClientID = client.ClientID, Key .ClientName = client.ClientName}
This returns the generic Enumerator result, however
Dim qClients As IEnumerable(Of DataRow) = From row In dtMatrix
Group row By client = New With {Key .ClientID = row("ClientID"), Key .ClientName = row("ClientName")} Into Group
Select New With {Key .ClientID = client.ClientID, Key .ClientName = client.ClientName}
Throws an exception
Unable to cast object of type... to type
'System.Collections.Generic.IEnumerable`1[System.Data.DataRow]'.
I will be happy to paste the whole error message if it will add more clarity.
My base assumption is that the DataTable should allow the cast to occur inherently as it is the object being queried. However this does not seem to be the case. Have I constructed my query incorrectly? (Framework 4.6.2)

Answer 1

You can use OfType on the Rows property of the DataTable:
Dim dtMatrix As DataTable = New DataTable()
'' Populate code goes here...
Dim dtRows As IEnumerable(Of DataRow) = dtMatrix.Rows.OfType(Of DataRow)()
The Rows property returns a DataRowCollection, that implements (through inheritance) the IEnumerable interface but not the IEnumerable(Of T) interface, that's why you can't use most of linq over it directly.

Answer 2

The following extension uses Reflection to create a new DataTable and create DataColumns in it that match the properties and fields of the type passed in. In general, if you are creating anonymous types in LINQ, you can't just convert to a DataRow which must be tied to a DataTable which must already have matching columns. I went ahead and wrote a second extension to DataTable that adds an IEnumerable<T> with matching field/property names to it.
Public Module Ext
<Extension()>
Public Function GetValue(member As MemberInfo, srcObject As Object) As Object
If TypeOf member Is FieldInfo Then
Return DirectCast(member, FieldInfo).GetValue(srcObject)
ElseIf TypeOf member Is PropertyInfo Then
Return DirectCast(member, PropertyInfo).GetValue(srcObject)
Else
Throw New ArgumentException("MemberInfo must be of type FieldInfo or PropertyInfo", Nameof(member))
End If
End Function
<Extension()>
Public Function GetMemberType(member As MemberInfo) As Type
If TypeOf member Is FieldInfo Then
Return DirectCast(member, FieldInfo).FieldType
ElseIf TypeOf member Is PropertyInfo Then
Return DirectCast(member, PropertyInfo).PropertyType
ElseIf TypeOf member Is EventInfo Then
Return DirectCast(member, EventInfo).EventHandlerType
Else
Throw New ArgumentException("MemberInfo must be of type FieldInfo, PropertyInfo or EventInfo", Nameof(member))
End If
End Function
<Extension()>
Public Function ToDataTable(Of T)(rows As IEnumerable(Of T)) As DataTable
Dim dt = New DataTable
If (rows.Any()) Then
Dim rowType = rows.First().GetType()
Dim memberInfos = rowType.GetProperties.Cast(Of MemberInfo)().Concat(rowType.GetFields).ToArray()
For Each info In memberInfos
dt.Columns.Add(New DataColumn(info.Name, info.GetMemberType()))
Next
For Each r In rows
dt.Rows.Add(memberInfos.Select(Function (i) i.GetValue(r)).ToArray())
Next
End If
Return dt
End Function
<Extension()>
Public Function AddObjects(Of T)(dt As DataTable, rows As IEnumerable(Of T))
If (rows.Any()) Then
Dim rowType = rows.First().GetType()
Dim memberInfos = rowType.GetProperties().Cast(Of MemberInfo)().Concat(rowType.GetFields()).ToArray()
For Each r In rows
Dim newRow = dt.NewRow()
For Each memberInfo In memberInfos
newRow(memberInfo.Name) = memberInfo.GetValue(r)
Next
dt.Rows.Add(newRow)
Next
End If
Return dt
End Function
End Module
Note that I write in C# and translated this from my C# extension. It is untested but compiles.
Using the extension, you should be able to get a DataTable from your qClients by:
Dim dtClients = qClients.ToDataTable()